The present invention relates to an apparatus for determining the concentrations of n hemoglobin derivatives in a sample of undiluted, unhemolyzed whole blood provided in a cuvette, including a device to produce a collimated primary light beam with at least n substantially monochromatic, narrow-band components of different wavelengths, and a detection device for measurement of the radiation passing through the cuvette, as well as an evaluation device connected with the detection device.